Abstract: The effects of aryl substituents on the stannic chloride-catalysed cyclisation of aryl cyclopropyl ketones (1) to aryl tetralones (2) are consistent with the formation of a benzyl carbocation intermediate (8) or a cyclic oxonium ion intermediate (12). The secondary alcohols (3), occasionally formed as side-products, are derived from this intermediate. Tetralone formation by a concerted pathway is disproved.

Abstract: Although many techniques are known which allow one to compare the stabilities of solution carbocations, that involving the intermolecular competition for a hydride ion is conceptually (but not expe...

Abstract: Rate constants have been measured for the thermal decomposition in diphenyl ether at 383–433 K of the carbamates of congested tertiary aliphatic alcohols (1)–(4) which are more reactive than any carbamates previously studied. The effects of structural change among (1)–(4) or of variation in substituent at the tertiary carbon atom are inconsistent with a predominantly carbocation type of mechanism. Kinetic deuterium isotope effects (k.i.e.) upon the methyl derivatives are unambiguously primary (2.2–2.6 at 400 K) and clearly indicate extensive C–H fission in the rate-determining step. These results contrast with the previous interpretation of the k.i.e in decompositions of CH3C6H4NHCO2But for which rate-determining C–O fission was proposed. Reinterpretation of the earlier data in terms of superimposed primary and secondary isotope effects leads to results in agreement with the new data and with the product isotope effects. Phenyl substituents, however, increase the carbocationic character of the transition state, but this mechanistic change does not cause the reactivity to be higher than that of the congested derivatives there is, therefore no relationship between the isotope effect and the reactivity.

Abstract: The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 686. DOI:10.1002/anie.198206860

Abstract: Methyl substitution of polycyclic aromatic hydrocarbons is known to induce substantial variations in carcinogenicity. The "Bay-region" theory relates carcinogenicity of polycyclic aromatic hydrocarbons to ease of formation of a triol carbocation from a bay-region diol-epoxide. It is shown that an examination of certain simple consequences of molecular orbital theory enables one to identify certain methyl substitutions that do not enhance ease of carbocation formation and hence are the least carcinogenically activating.

Abstract: Irradiation of exo—2—benzonorbornenyl chloride and mesylate, with 254 nm light, leads to facile cleavage of the C—Cl and 0—Ms groups (eq. 1 and 2). The reactions derive from the aryl excited singlet state, involve radical as well as ("hot') carbocation intermediates, and proceed more effectively with the exo, rather than endo, isomers. In the [2.2.2] series (eq. 3 and 4), fragmentation again occurs but the endo chloride is now the more reactive isomer. A new * approach to rationalizing the "n,TF " photochemistry of ketones and aldehydes is presented. The method utilizes the * "HOMO dictated" nature of "n-'rr transformations, and is applied to the Norrish Types I and II photofragmentations (Fig. 5 and 6) and intermolecular hydrogen abstraction (Fig. 7). These Figures illustrate the use of newly developed "Delta Plots", i.e. contour diagrams which allow one to visualize the changes in electron density resulting from electronic excitation.

Abstract: Oct-1-ene and cis- and trans-oct-4-enes were treated with p-nitrobenzenesulphonic acid in acetic acid (0.1M) at 25°, when addition of the sulphonic acid and of acetic acid and the direct formation of isomeric octenes were all observed. At a greater rate, the covalent ester underwent acetolysis. The kinetically controlled mixture of products from the olefins was deduced from analyses at varying small degrees of reaction, extrapolating to zero conversion, and correcting for the products known to have been formed via covalent arenesulphonate. The results for cis-oct-4-ene proved that the lifetime of the 4-octyl cation in acetic acid is short compared with the time for rotation around a C3H7CH–CH2C3H7 bond.

Abstract: The effects of a series of cationic and anionic surfactants of increasing n-alkyl chainleijigth on the reaction of ethyl violet carbonium ion (EV+) with hydroxide ion have been studied and the results have been analysed quantitativelye Extent of catalysis by hexadecyl-, tetradecyl-, and dodecyltrimethylammonium bromides at the rate maximum was found to be 59, 31 and 4.8 fold respectivelye Anionic surfactants viz. tetradecyl-, dodecyl-, decyl-, and octyl sodium sulfates inhibited the reaction significantly even at very low concentrations. Catalysis by non-ionic micelles of Brij-35 was dependent on hydroxide ion concentration. The extent of catalysis of the reactions of various triphenylmethane dye carbonium ions with hydroxide ion has been correlated to the substrate hydrophobicity. Added counter- ions to the surfactant and solvents decreased the efficiency of micelles. Effect of temperature on micelle catalysed and inhibited reactions has been studied and the micellar effects have been discussed in terms of thermodynamic quantities of activation.

Abstract: Solvolysis of 2αH-pinan-3α-yl toluene-p-sulphonate has been shown to proceed with concomitant 1,2-hydride shift to give the pinan-2-yl carbocation. Contrary to earlier reports, this species reacts normally to give, in good yield, pinan-2-yl substitution products. In contrast the pinan-3-ylamines react via a similar route, but give much smaller amounts of pinan-2-yl products. The usual reasons for differences between solvolysis and deamination (i.e. the intermediacy of diazonium ions and/or high-energy ions) can be discounted, and possible reasons for the differences in behaviour are discussed.